Cable networks have been expanding beyond the basic delivery of television signals for which they were originally designed. Today they can carry data for internet and other communications as well as voice signals for the traditional telephone function. Competitive delivery of these services is requiring ever increasing data rates to the user.
At present, signals are transmitted over cable networks in the U.S. over a frequency band that spans about 1 GHz. Upstream traffic typically extends over a band from 5-85 MHz, whereas downstream traffic extends over a band that can range from 54-1002 MHz (the two bands may not overlap). The band is separated into channels that are 6 MHz wide.
Increased data rates are specified by just about every next-generation standard, including the Data Over Cable Service Interface Specifications (DOCSIS) 3.0 standard, the Society for Cable Telecommunications Engineers (SCTE) 40 standard, and the Comcast Residential Network Gateway (RNG) standard, all of which are incorporated herein by reference in their entireties. Although digital modulation increases the efficiency (and hence the data rate) of a given channel, the channel bandwidth places a fundamental limit on a given channel's information-carrying capacity. The only way to meet the new specifications is to increase the total bandwidth available for data transmission.
One way to increase the effective data rate is to aggregate, or bond, channels together. For example, bonding together four channels each operating at 40 Mbps yields an effective data rate of 160 Mbps. In addition to increasing demand for higher data rates, demand is also growing for having a greater number of video channels available at the customers' premises. With picture-in-picture, recording-while-viewing, and multiple simultaneous viewers watching different channels in a household, the number of simultaneous video channels required per household is increasing. Combined with the several channels required for data, the total number of simultaneous channels can reach 6-8 or higher in the future.
In conventional cable gateways, each channel is filtered, downconverted, and demodulated with a narrowband analog tuner. Because each channel requires its own tuner, however, cable gateways that use multiple tuners consume considerable power, dissipate that power as heat, and are therefore costly to operate.